Severe perinatal ischemia can lead to brain injury and dysfunction. Although hypoxia- and hypoglycemia-mediated loss of synaptic functions and neuronal death are major components of brain ischemia pathophysiology, effective clinical neuroprotection for this damage remains elusive. Our preliminary experiments provide support for the novel hypothesis that gap junctions, the intercellular channels that mediate electrical synchrony and metabolic cooperation between apposed cells, participate in propagation of neuronal damage and death following global ischemia in developing brain. Evidence indicates that cells injured by ischemic brain insults are linked to surrounding, less-affected cells, and that this "bystander effect" expands the volume of a brain ischemic injury over time. The overall goal of the proposed studies is to characterize the role of neuronal and astrocytic gap junction channels in propagating delayed neuronal death mediated by ischemic insults in field CA1 of the hippocampus. The broad hypotheses to be tested are that: (1) gap junction-mediated signaling can amplify the extent of ischemic injury, and (2) gap junction blockade will reduce the extent of cell death of CA1 pyramidal neurons and astrocytes following ischemia This application proposes to address these questions using both hippocampal organotypic slice cultures and in vivo studies performed in newborn rodents delivered by Caesarean-section and subjected to immediate transient global hypoxia, prior to removal from the uterus and commencement of respiration. Two complementary strategies will be used: First, molecular biological and electrophysiological techniques will evaluate the extent of ischemia-induced injury in slice cultures from wild type mice. Second, the extent of damage will be compared to mice in which the major neuronal (connexin36) and astrocytic (connexin43) gap junction proteins have been genetically reduced (Cx36-/+ and Cx43-/+) or ablated (Cx36 and Cx43 knockouts), and under conditions in which the ischemic event occurs when Cx43 and Cx36 are differentially blocked pharmacologically. These studies are expected to provide mechanistic insights into the extent of neuronal death following brain global ischemia and to have significant therapeutic application in the treatment of long-term sequelae of ischemia in perinatal brain.